The present invention relates to a method of manufacturing lenses and particularly to such a method for producing lenses having an increased depth of focus.
A system for storage and retrieval of information at extremely high densities is described and claimed in U.S. Pat. No. 3,501,586 granted to James T. Russell on Mar. 17, 1970, entitled "Analog to Digital to Optical Photographic Recording and Playback System" and assigned to the assignee of the present invention. In such a system a single pulsed light source is focused to an extremely small focal spot which is optically scanned over a sensitive medium for either the recording or playback of information. Audio or video information can be recorded through the conversion of the analog information to digital information used to modulate the light source whereby the record appears as a multiplicity of digit-representing spots arranged on the medium with high packing density. The positioning of optical elements and the sensitive medium tends to be critical for making sure the record is not blurred or out of focus. A small spot size for a lens or the like ordinarily implies a short depth of focus so that the recording medium must be accurately situated and substantially flat to prevent the blurring or overlapping of the recorded information.
In a particular instance, information may be recorded with a scanning disc which is rotated past a photosensitive plate, wherein relative linear movement is also provided between the scanning disc and the photosensitive plate. A plurality of microscope objectives are positioned upon the scanning disc, each one in turn receiving a beam of light and tracing an arcuate path across the face of the photosensitive plate whereby paths of digital spots may be recorded on such plate. As will be appreciated by those skilled in the art, the depth of focus of the microscope objectives is such that the spacing between the scanning disc and the photosensitive plate must be accurately predetermined.
Holographic lens means have also been employed for scanning a beam of light over a record, such as for recording or playing back information on a photosensitive film or the like. The holographic lens means can be rotated in a scanner for describing the path of a light beam across the recording element. Each such holographic lens means is suitably formed in the same manner as any other hologram by directing a coherent object beam and reference beam toward the location where the lens is to be formed, i.e., upon a photosensitive scanning element or disc. The scanning element is developed to reproduce the interference pattern of said object beam and reference beam and is then capable of optically reconstructing the "object" from which the hologram was formed. In the case of the conventional holographic lens, the "object" would suitably comprise a point source whereby the resulting hologram will reconstruct the point source at a given focal length for scanning a record. However, as in the case of a scanner employing microscope objectives for reading or recording spots, the scanner employing holographic lens means will also be subject to close tolerance requirements on positioning and flatness of the record to prevent an out-of-focus or blurred record, or alternatively, inability to read the record with accuracy.